1. Field of the Invention
The invention relates to a method of assigning service channel to traffic in communication system in which a subscriber""s terminal is in communication with a base station through radio signals.
2. Description of the Related Art
There have been suggested many methods of assigning channel to traffic in communication system. For instance, such methods are suggested in Japanese Unexamined Patent Publications Nos. 6-189361, 6-509456 and 9-187065, and Japanese Patent No. 2760375.
In accordance with those methods, radio-signal channel is assigned to traffic in an order of calling, regardless of whether service rank is high or low, for instance, in a cellular phone.
However, the above-mentioned methods in which radio-signal channel is assigned to traffic in an order of calling include a problem that if radio-channel are occupied by traffics each having a low service rank, it would be impossible to assign radio-signal channel to traffic having a high service rank.
For instance, traffic having a low service rank includes a general call, and traffic having a high service rank includes an urgent call, a hot line and a priority call. In accordance with the above-mentioned methods, if radio-signal channels were occupied by general calls, it would be impossible to assign radio-signal channel to an urgent call.
In one method, if radio-signal channels are occupied by traffics each having a low service rank, and accordingly, radio-signal channel cannot be assigned to traffic having a high service rank, radio lines may be all cancelled in order to let traffic having a high service rank have priority over traffic having a low service rank. Thereafter, traffics having a low service rank are refused to receive.
However, there is traffic which has a low service rank, but includes very important communication. Such traffic is also interrupted in the above-mentioned method.
In view of the above-mentioned problem in the prior art, it is an object of the present invention to provide a method of assigning service channel to traffic, which method is capable of assigning radio-signal channel to traffic having a high service rank, even if radio-signal channels are all occupied by traffics each having a low service rank.
In one aspect of the present invention, there is provided a method of assigning service channel to traffic in communication system in which a subscriber""s terminal is in communication with a base station through radio signals, including the steps of (a) reserving the predetermined number of channels in advance for traffic having a predetermined service rank, and (b) assigning channel preserved in advance, to the traffic having a predetermined service rank, only when there is no channel to be assigned to the traffic having a predetermined service rank.
In accordance with this method, service channels are reserved in advance only for traffic having a predetermined service rank, for instance, traffic having a high service rank. The thus reserved service channels are assigned only to traffic having the predetermined service rank, and not assigned to other traffics. Hence, even if traffic having the predetermined service rank is received after channels other than the above-mentioned reserved channels are occupied by traffics other than traffic having the predetermined service rank, the reserved service channels are assigned to traffic having the predetermined service rank.
Thus, the method solves the above-mentioned problem that it is impossible to assign radio-signal channel to an urgent call, a hot line or a priority call, because radio lines are all occupied by general calls.
It is preferable that the method further includes the step of, if channel having been assigned to traffic other than the traffic having a predetermined service rank is released, after all channels have been assigned, reserving the released channel as channel to be assigned only to the traffic having a predetermined service rank.
In accordance with this embodiment, it would be possible to reserve service channel to be assigned to traffic having the predetermined service rank, even after all channels are occupied by traffics other than the traffic having the predetermined service rank.
In another aspect of the present invention, there is provided a communication system in which a subscriber""s terminal is in communication with a base station through radio signals, wherein the base station in advance reserves the predetermined number of channels to be assigned to traffic having a predetermined service rank, only when there is no channel to be assigned to the traffic having a predetermined service rank, the subscriber""s terminal transmits a first signal to the base station to request the base station to assign channel to the subscriber""s terminal, the base station, on receipt of the first signal, transmits a second signal to the subscriber""s terminal which second signal is indicative of free channel to be assigned to the subscriber""s terminal, among the predetermined number of channels, and the subscriber""s terminal, on receipt of the second signal, assigns channel identified by the second signal to the traffic having a predetermined service rank.
This communication system provides the same advantages as those provided by the above-mentioned method.
It is preferable that if channel having been assigned to traffic other than the traffic having a predetermined service rank is released, after all channels have been assigned, the base station reserves the released channel as channel to be assigned only to the traffic having a predetermined service rank.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.